// 运算符
class AddressBookBuilder {
  String name;
  String email;
  String phone;

  String build () {
    return '${name}: ${email}: ${phone}';
  }
}

class PhoneNumberBuilder {
  String number;
  String label;

  String build () {
    return '${label}: ${number}';
  }
}

main () {
  // 级联运算符 (..)
  final addressBook = (AddressBookBuilder()
      ..name = 'jenny'
      ..email = 'jenny@example.com'
      ..phone = (PhoneNumberBuilder()
            ..number = '415-555-0100'
            ..label = 'home')
          .build())
    .build();
}